The present invention relates generally to stator assemblies and more specifically to a stator flux ring having fastenable pole pieces and a method for making same.
Dynamoelectric machines, such as electric motors, are ubiquitous in electro-mechanical products, such as in air compressors, refrigerators, washing machines, dishwashers and the like. It is important to be able to manufacture such motors efficiently and at a minimum cost.
Conventional motors include a stator core and a rotor that typically rotates within the stator core. Known stator cores are formed by stacking a plurality of stamped ferromagnetic discs to form a yoke. The discs are laminated and stacked in an aligned relation. It is also known to form a core by continuously winding a lanced strip of ferromagnetic material edgewise about an arbor. The strip is continuous and may have pole cavities or teeth formed therein. Stator windings are then wound about the teeth, which are generally distributed evenly about the inner circumference of the stator core. U.S. Pat. No. 4,578,853 to Wurth issued on Apr. 1, 1986 discloses a stator core formed of stacked laminations. However, the number of poles are fixed. Additionally, because the poles are integrally formed with the laminations, their shape cannot be changed with modifying the basic lamination.
It is also known to use adhesive material to fasten pole pieces to laminations comprising the stator core. Such methods are relatively expensive due to labor costs associated with the gluing operation. Additional costs are incurred because the stator must remain immobile until the adhesive cures. Alternately, the stator core is baked to cure the adhesive, which also increases the costs of such methods.
The disadvantages of known stator cores and method of manufacturing such stator cores are substantially overcome with the present invention by providing a novel stator flux ring having fastenable pole pieces. The present flux ring and method permits a stator core or yoke to be formed economically and with high reliability. Additionally, stator cores manufactured according to the present method provide manufacturing flexibility because pole pieces of different sizes and shapes may be used with existing flux rings. As described above, it is known to integrally form the pole pieces as teeth or projections of the stamped laminations. Accordingly, the pole has a constant size and shape. This may increase inventory and stocking costs because a slight variation in motor requirements may dictate that an entirely new stator lamination be used, which must also be stocked. For example, if a particular stator yoke permits the pole to be wound with a maximum of 30 turns of 20 gauge wire, then the number of turns using the same gauge wire cannot be exceeded. Accordingly each motor may require different flux ring construction.
In the present invention, however, if for example, a motor application requires 50 turns of 20 gauge wire, a pole piece of a different size or shape may be attached to the flux ring. A slightly larger pole piece, or one having a larger outward flair, may accommodate the additional turns of wire. In this way, the same flux ring may be used to manufacture many different stator cores because the pole pieces are separate from the flux ring to which they are attached. Additionally, the pole pieces are formed or shaped separately from the strip of material that forms the core. This significantly reduces the amount of material wasted in the stamping process compared to methods having the pole pieces integrally formed with the flux ring.
More specifically, the stator core of one embodiment of the present invention is in the form of helical convolutions of a continuous strip ferromagnetic material that is wound edgewise to form a stator core. The core includes a plurality of flux rings having a plurality of spaced apart integrally formed lugs outwardly extending along an outer circumferential edge of the flux ring, where each lug has deformable edges. Pole pieces are fastened to the flux rings, and the flux rings have a body portion defined by an annular front portion. The body portion also has first and second arms that project laterally from the body portion and extend along a portion of the outer circumferential edge of the flux ring when fixed thereto. Each pole piece is operatively secured between two adjacent lugs and abuts the outer circumferential edge of the flux ring. When secured, the arms abut the corresponding deformable edges of the lug. A portion of the deformable edges of the lug are then deformed and expand to overlap the arms and wedge the pole piece between the circumferential edge and the lugs.